Adjuvants administered as a mixture with vaccine antigens activate natural immunity and help the induction of antigen-specific immune response via antigen presentation.
Various adjuvants for animal experiments are known. Common compounds of non-biological origin are used as adjuvants due to their properties of adsorbing antigens such as pathogens, and examples of such a compound include sodium hydroxide, aluminum hydroxide, calcium phosphate, alum, and a carboxyvinyl polymer. However, these precipitating adjuvants are prone to cause injection site induration. Oily substances such as liquid paraffin, lanolin, and Freund's adjuvant are also used as adjuvants due to their properties of encapsulating an aqueous antigen solution and forming micelles. However, since a mixture of such an oil-based adjuvant and a vaccine antigen forms an emulsion containing micelles, the mixture has a high viscosity, which may cause injection pain, and is prone to cause injection site induration.
Besides the above adjuvants, a relatively safe bacterium Mycobacterium bovis (BCG), which hardly causes endotoxin shock or the like, is also used as an adjuvant. However, BCG bacterial bodies are prone to cause an ulcer at the injection site.
Since a highly effective adjuvant generally has a strong toxicity, development of a safe and effective adjuvant has been desired.
JP-2008-100919-A describes, as an adjuvant of natural product origin, a nucleic acid/polysaccharide complex composed of a CpG oligonucleotide having a natural phosphodiester backbone and a poly(dA) tail and of a β-1,3-glucan having a molecular weight of 25000 or more. This patent literature suggests that this nucleic acid/polysaccharide complex can promote production of cytokines and antibodies that establish dominance of Th1 cell activity and therefore the complex can be used as an immunoadjuvant.